Over 20% of the population exhibits incomplete stereopsis, whereby binocular cues for distance are not fully utilized. These individuals are said to possess anomalous stereoscopic depth perception. By determining which physical cues are not utilized by these individuals but are used by others, we may deduce the nature of the physiologic mechanisms that underly stereopsis. Of particular interest is whether anomalous stereoscopic depth perception represents a reduction of the normal stereoscopic mechanisms. Complementary work in neuroanatomy is also underway to determine the physiologic correlates of anomalous stereoscopic depth perception in both cats and men. Primary emphasis is currently on the role of the lateral geniculate nucleus and the relation between anomalous geniculate structure, stereopsis and crosseyedness.